1. Field of the Invention
A method of stabilizing wet process phosphoric acid containing acid soluble impurities preparatory to solvent extraction.
2. Brief Description of the Prior Art
Wet process phosphoric acid is prepared by reacting phosphate rock with sulfuric acid. The reaction product is filtered and then washed to yield a crude aqueous acidic solution known as "wet process phosphoric acid." The crude aqueous product contains significant amounts of dissolved impurities. Impurities which almost always are present are calcium, sodium, potassium, iron, aluminum and magnesium cations and sulfate and fluorosilicate anions. The wet process phosphoric acid also has been found to contain either or both vanadium and uranium.
Numerous processes have been developed to recover either or both vanadium and uranium from wet process phosphoric acid by solvent extraction using organic extractants. Generally, such processes provide a method of contacting the wet process phosphoric acid with the organic extractant to form a complex which then separates either or both the vanadium and uranium therefrom. The organic extractant then is separated from the wet process phosphoric acid, scrubbed with water in some processes and then stripped of either or both the vanadium and uranium by contact with a stripping solution.
The presence of the soluble impurities, particularly calcium sulfate and sodium or potassium fluorosilicates, in the wet process phosphoric acid has presented certain difficulties in the successful extraction and recovery of either or both the vanadium and uranium. During solvent extraction treatment of the wet process phosphoric acid, the calcium sulfate and other impurities often precipitate forming sediments or scales within the extraction process apparatus. The sediments contaminate the selective organic extractants and limit their ability to separate the vanadium and uranium from the wet process phosphoric acid. The scales which form on the apparatus result in apparatus plugging and other operational difficulties.
It is desirable to provide a method for preparing wet process phosphoric acid from which either or both vanadium and uranium may be recovered by organic solvent extraction, the wet process phosphoric acid having been stabilized to prevent the precipitation of sediments or scales of impurities during said recovery.